1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and, more particularly, it relates to a discharge recovery or restoring device for an ink jet recording apparatus, which is provided with a cap capable of covering a recording liquid discharge surface to prevent the jamming of discharge openings of a recording head and to prepare initial charge or introduction of a recording liquid and to permit suction of ink (recording liquid) and/or air.
2. Related Background Art
In a recording head used with an ink jet recording apparatus, flying drops of recording liquid are created by discharging the recording liquid from minute or small discharge ports or openings each having a diameter of the order of about 40-50 .mu.m. However, with such a construction, there is a tendency for bubbles to accumulate in liquid passages into which the recording liquid is introduced, and dust stuck about and around the discharge openings and/or solidification of the recording liquid may cause non-discharge of the recording liquid (from the discharge openings) and deviation of the discharged liquid drops with respect to a recording medium.
For these reasons, in the past, as shown in U.S. Pat. No. 4,600,931 in order to eliminate the above drawbacks and to facilitate the initial introduction of the recording liquid to the liquid passages of the recording head, for example, when the recording head is used again after it is dormant for a long time, a suction operation indentified as a restoring operation has been utilized by covering the recording liquid discharge face of the recording head by means of a cap member.
Such a cap member was so constructed that the recording head, brought into a home position was covered by the cap member and the recording liquid was sucked through the discharge openings arranged on the discharge face by means of an appropriate suction means communicating with the cap member.
FIG. 1 shows an example of a cap member of the conventional discharge restoring device, such as shown in the U.K. Patent Laid-Open No. GB-2184066 A. This Figure shows a condition that a front plate 3 of a recording head 2 is covered by a cap member 1. The recording head 2 includes a plurality of discharge openings 4 arranged on the front plate 3 along an up-and-down direction, and a plurality of liquid passages 6 for communicating a common liquid chamber 5 with the corresponding discharge openings to direct the recording liquid in the liquid chamber 5 to the discharge openings 4. When the recording operation is started, the recording liquid is discharged from the discharge openings 4 by means of discharge energy generating means (not shown) such as piezo-electrical elements, electrical-thermal converters and the like.
When the cap member 1 is mounted on the front plate 3 of the recording head 2 (as shown), a space 8 defined by the plate 3 and cover 1 is sealed fluid-tight with respect to the atmosphere by engaging an elastic seal 7 (such as a silicone rubber ring, butyl rubber ring and the like) arranged on a peripheral edge of the cap member 1 with the front plate 3. The cap member 1 has a communication port 9 at a lower portion of the space or cavity 8, which port 9 is communicated with an external suction pump 10. In this condition, air in the cavity 8 is sucked through the communication port 9 by the suction pump 10 to create pressure lower than atmospheric pressure in the cavity 8, thus introducing the recording liquid into the cavity 8 through the discharge openings 4 and then exhausting the recording liquid from the cavity to an appropriate exhaust liquid tank (not shown) by the action of the suction pump 10.
By the way, in a conventional restoring device of this kind, the communication port 9 was positioned in the lower portion of the cavity 8 of the cap member 1 so as not to leave the recording liquid after the liquid was drawn through the communication port, thus preventing the liquid from dropping out of the cavity, and preventing contamination of the apparatus, when the cap member 1 was separated from the front plate of the recording head 2.
However, when a recent multi-nozzle recording head having a great number (for example, 128) of the liquid passages and discharge openings is used, for example during the initial introduction of the recording liquid into the liquid chamber 5, as shown by a hatched line in FIG. 1, the recording liquid is drawn or sucked through the discharge openings situated in the lower portion (i.e., not through all of the discharge openings) before the liquid chamber 5 is completely filled with the recording liquid, with the result that the restoring operation has been completed before the whole liquid chamber is filled with the recording liquid (i.e., before the discharge openings situated in the upper portion are filled with the recording liquid). Thus, in the conventional multi-nozzle recording head, there was a problem that, when the recording operation was initiated after such restoring operation, the recording liquid was not discharged from the discharge openings situated in the upper portion, whereby complete images as desired could not be recorded on the recording medium.
On the other hand, in a recording head of a full-line type recording apparatus in which recording operation is performed by discharging the recording liquid from the discharge openings of the recording head while it is stationary with respect to the recording medium, a great number (for example, about 1792) of the discharge openings are arranged substantially along a single line.
In such a recording head of the full-line type, since the array of the discharge openings extends substantially in a horizontal direction, the distance between two discharge openings situated on both ends of the array is relatively large, and accordingly, the length of the common chamber which must be communicated with all of the discharge openings is also relatively large in the horizontal direction. Thus, also in this case, if, by utilizing the suction effect through the cap member, the recording liquid is introduced into the recording head and the restoring operation is performed as in the above-mentioned case, there arises the same problem as described above.
That is to say, if the communication port leading to the suction pump is provided at the left end of the cap member, the liquid passages situated at the right side of the recording head will not be filled with the recording liquid, whereas if the communication port is provided at the right end of the cap member, the liquid passages situated at the left side of the head will not be filled with the recording liquid.